crooked toilet rough, flange not flat

i inherited a toilet rough-in that came out of the floor at an angle. i dry-fitted several different flanges and one of them seemed like it would slide down flat to the floor. but after i glued it up and took my foot off it, one side of the flange is on the floor but the other side is 1/4" or more off the floor. i set my Toto on it and the toilet isn't sitting tight to the floor.

taking up some floor / subfloor isn't out of the question but space is tight in the floor and i don't see that i can make the riser plumb.

my thought now is to flush cut the flange at floor level and use an inside flange. (when dry-fitting different flanges, the inside also sat tight to the floor.)
this is ABS, 3". it seems like reducing the size of the pipe isn't a great idea, but i measured and the inside diameter of the inside flange is still larger than the inside diameter of the horn on my Toto Drake.
so i should go for it, yes?

Not a good idea for the reason you mention. Using an inside flange on a 4" pipe is OK, but not a 3". You should do what you have to do to get the flange to set level on top of the finished floor. I don't thing the 3" inside flange would set level anyway.

Another option would be to use another Toto toilet model that uses a unifit rough-in if you can still return the drake. Sure the toilet would be a bit more expensive, but it would definitely be nicer in your home. You could pop a shim under the raised side before you anchor the flange, and then any offset could be addressed by the unifit flange.

A internal fit flange wouldn't solve your problem as Gary mentioned. The pipe is not rising plumb, so your only option to fix it as far as I can see, is to reinstall the pipe.